1. Field of the Invention
The present invention relates to an apparatus for forming images, a method of controlling the apparatus and a storage medium. More particularly, the present invention relates to an image forming apparatus for forming a visible image on a predetermined recording medium, a method of controlling the apparatus, and a storage medium storing a program used for forming the visible image.
2. Description of the Related Art
An electrophotographic printer will be described as one example of a conventional image forming apparatus.
First, the electrophotographic printer employs, as an image signal, a signal with a resolution of 400 dpi. Then, a gradation image reproducing section of the printer sets the resolution of an output image under conditions favorable for reproducing intermediate tones, i.e., 200 dpi in the direction of main scan (direction in which an image is scanned by a laser) and 400 dpi in the direction of sub-scan (direction perpendicular to the direction of main scan). On the other hand, a character/line image reproducing section of the printer sets the resolution of an output image under conditions favorable for reproducing character edges, i.e., 400 dpi in the direction of main scan and 400 dpi in the direction of sub-scan.
Further, in certain copying machines, an image is reproduced with pixel resolution of 200 dpi in the direction of main scan and 400 dpi in the direction of sub-scan in a mode where an emphasis is placed on gradation, such as a printed photo mode or a photographic paper photo mode, and with pixel resolution of 400 dpi in the direction of main scan and 400 dpi in the direction of sub-scan in a mode where an emphasis is placed on edge reproduction of character/line images, such as a character mode or a map mode.
Additionally, in a character/photo mode, an edge portion of characters and thin lines is determined as to whether it represents an area of a gradation image or a character/line image. Then, the area determined as being a gradation image is reproduced with pixel resolution of 200 dpi in the direction of main scan and 400 dpi in the direction of sub-scan, while the area determined as being a character/line image is reproduced with pixel resolution of 400 dpi in the direction of main scan and 400 dpi in the direction of sub-scan.
Even for a gradation image, however, persons tend to very often look at the image from a short distance when the image size is small.
This raises a problem that when the resolution is lowered by reason of a gradation image as mentioned above, the contours of dots now becomes conspicuous and image quality deteriorates contrary to the user""s intention. In particular, when the image is observed at a distance of about 15 cm from the image to the viewer""s eye, the presence of each dot is visually recognized and such problem is more conspicuous.
In view of the above-stated problem in the art, an object of the present invention is to provide an apparatus for forming images, a method of controlling the apparatus, and a storage medium, with which pixel resolution is relatively raised when the size of an image to be output for recording is small, enabling even a gradation image to be visually perceived with satisfactory quality when observed from a short distance.
To achieve the above object, an apparatus for forming images according to the present invention is constructed as follows. Specifically, in an image forming apparatus for forming a visible image on a predetermined recording medium based on input digital image data, the apparatus comprises image forming means capable of forming visible images with multiple degrees of resolution, and control means for controlling the image forming means to select one of the multiple degrees of resolution depending on the size of an image area to be formed by the image forming means.
In the above image forming apparatus, preferably, the control means controls the image forming means to select one of the multiple degrees of resolution depending on the size of a recording medium. With this feature, optimum resolution can be simply set when an original image is recorded on a smaller scale, for example.
In the above case, preferably, the control means controls the image forming means to select the higher one of the multiple degrees of resolution as the size of a recording medium is reduced. With this feature, even when a printed image is observed from a short distance, the contours of dots become less conspicuous and the image can be visually recognized with good quality.
The image forming apparatus may further comprise document reading means, and designating means for designating an effective area in a document read by the document reading means, the control means controlling the image forming means to select one of the multiple degrees of resolution depending on the size of the effective area designated by the designating means. In this case, preferably, the control means controls the image forming means to select the higher one of the multiple degrees of resolution as the effective area designated by the designating means is reduced.
Alternatively, the image forming apparatus may further comprise document reading means, and preparing means for preparing a histogram of density distribution in a document read by the document reading means, the control means controlling the image forming means to select one of the multiple degrees of resolution depending on the density distribution given by the prepared histogram.
Other objects and forms of the present invention will be apparent from the following description made with reference to the drawings and the attached claims.